Eat. Yes, eat. When I get stuck for several days, even though I am eating considerably less than I am burning, eating extra calories for a day helps get things moving in the right direction again....kinda like it reassures my body that there IS plenty of food available and I'm NOT starving it, that it doesn't need to hang on to everything I'm giving it. Try it tomorrow....eat an extra 300-400 calories over what your body is accustomed to and see if it doesn't kick the body back into gear.
Yo've been loosing 2.5 lbs a week not even starting from an exceptionally high level so it could be something like having over lost water weight in the start now balancing out. In any event considering the speed you have achieved I wouldn't bother worrying about a one week glich.
You are severely under eating for the amount of calories you are burning. You should eat way more and have a much, much lower deficit. Especially if you are exercising so much.
Also, a week is not a statistically significant amount of time.
Listen to armandounc. Your deficit should be like 250 cals a day or like 0.5 pounds a week, because you are at a healthy weight. Much more than that and your body will rebel (ie. 6500 deficit a week should be more like 1750 a week). Adjust accordingly.
I'm your height and have similar weight loss goals (I'm at 128 though right now).
I agree that you need to eat more. Also, while running is great are you doing anything else? Switching up your exercise routine is key to getting over plateaus. Maybe incorporate dancing, strength training, or something else 2 or 3 times a week into your routine. If you're only doing one workout your body eventually adapts to it and you stop making progress since they're not working as hard. More muscle = higher metabolism remember.
I agree with what everyone else is saying. I'm 42, 5'1.5 and 124 lbs. and am losing weight on 1400-1500 calories a day with at least one 1700 calorie day a week. Plus, I only work out about 3 days a week. You are younger and working out a lot so I would add at least a couple hundred calories a day to your intake. Also, try staggering your calories each day; 1400 one day, 1700 the next, and 1500 the following, and so forth.